Eukaryotes domain

As we will see, the evolutionary tree is bisected into a lower prokaryotic domain and an upper eukaryotic domain. The terms prokaryote and eukaryote refer to the most basic division between cell types. The fundamental difference is that eukaryotic cells contain a membrane-bounded nucleus, whereas prokaryotes do not. The cells of prokaryotes usually lack most of the other membrane-bounded organelles as well. Plants, fungi, and animals are eukaryotes, and bacteria are prokaryotes. The biochemical functions associated with organelles are frequently present in bacteria, but they are usually located on the inner plasma membrane. 

Plastocyanins are the most widely studied cupredoxins. They are one of the most abundant copper proteins in plant photosynthetic tissues. Plant plastocyanins have an intricate evolutionary history because of their ancient bacterial origin. It is currently well accepted that plants diverged from the main eukaryotic domain into a separate lineage when the unicellular, oxygen respiring common ancestor of the eukaryotes incorporated a prokaryotic endosymbiont, the cyanobacterial chloroplast. 

SMART (Simple Modular Architecture Research Tool) [12-14] is a Web-based resource used for the annotation of protein domains and the analysis of domain architectures, with particular emphasis on mobile eukaryotic domains. Extensive annotation for each domain family is available, providing information relating to function, subcellular localization, phyletic distribution and tertiary structure. The January 2002 release has added more than 200 hand-curated domain models. This brings the total to over 600 domain families that are widely represented among nuclear, signalling and extracellular proteins. Annotation now includes links to the Online Mendelian Inheritance in Man (OMIM) database in cases where a human disease is associated with one or more mutations in a particular domain, (http //smart, embl-heidelberg. de/help/smart about. shtml)... 

FerredoxinrNADP oxidoreductase (FNOR, EC 1.18.1.2) is a flavoenzyme that catalyzes electron transfer between the redox protein, ferredoxin, and the pyridine nucleotide coenzymes, NADP(H) and/or NAD(H). Enzymes of this type have been characterized from many organisms, including from both the bacterial and eukaryotic domains. " However, only one such enzyme has been purified from... 

The native form of chromatin in cells assumes a higher order stmcture called the 30-nm filament, which adopts a solenoidal stmcture where the 10-nm filament is arranged in a left-handed cod (Fig. 5). The negative supercoiling of the DNA is manifested by writhing the hehcal axis around the nucleosomes. Chromatin stmcture is an example of toroidal winding whereas eukaryotic chromosomes are linear, the chromatin stmctures, attached to a nuclear matrix, define separate closed-circular topological domains. 

In cyclic nucleotide-regulated channels, this domain serves as a high-affinity binding site for 3-5 cyclic monophosphates. The CNBD of channels has a significant sequence similarity to the CNBD of most other classes of eukaryotic cyclic nucleotide receptors and to the CNBD of the prokaryotic catabolite activator protein (CAP). The primary sequence of CNBDs consists of approximately 120 amino acid residues forming three a-helices (oA-aC) and eight (3-strands ( 31- 38). 

PAS domains are protein domains, encompassing about 250-300 amino acids, which in higher eukaryotes function as surfaces for both homotypic interactions... 

The Rel homology domain (RHD) is an evolutionarily conserved domain found in some eukaryotic transcription factors, including NF-kB, the nuclear factors of activated T-cells (NFATs) and the drosophila proteins Dif and Relish. Some of these transcription factors form... 

Ribosomes are ancient ribonucleoprotein complexes that are the sites of protein synthesis in living cells. Their core structures and fundamental functional mechanisms have been conserved throughout the three domains of life bacteria, archaea and eukaryotes. All ribosomes are organized into two subunits that are defined by their apparent sedimentation coefficient, measured in Svedberg units (S). There is a general... 

The third type of E3 ligases is represented by the polycomb protein 2 (Pc2), which was reported to enhance sumoylation of the substrate CtBP. N- and C-terminal domains in Pc2 that have been implicated in CtBP sumoylation do not resemble known E3 ligases. Like RanBP2, Pc2 expression is restricted to higher eukaryotes. 

Microtubules are universally present in eukaryotes from protozoa to the cells of higher animals and plants (Porter, 1966 Hardham and Gunning, 1978 Lloyd, 1987), but they are absent in mammalian erythrocytes and in prokaryotes. Microtubules participate in a number of cellular functions including the maintenance of cell shape and polarity, mitosis, cytokinesis, the positioning of organelles, intracellular transport to specific domains, axoplasmic transport, and cell locomotion. The diversity of microtubule fimctions suggests that not all microtubules are identical and that different classes of microtubules are present in different cell types or are localized in distinct domains in the same cell type (Ginzburg et al., 1989). 

The multiple sites that serve as origins for DNA replication in eukaryotes are poorly defined except in a few animal viruses and in yeast. However, it is clear that initiation is regulated both spatially and temporaUy, since clusters of adjacent sites initiate rephcation synchronously. There are suggestions that functional domains of chromatin replicate as intact units, implying that the origins of rephcation are specificaUy located with respect to transcription units. 

Kuriyan, J. and Cowburn, D., Modular peptide recognition domains in eukaryotic signaling, Annu. Rev. Biophys. Biomol. Struct., 26, 259-288, 1997. 

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